Not everyone knows when the origin of the third most abundant element in the universe appeared on Earth.
Understanding Oxygen on Earth
Oxygen is the most crucial element for the survival of humanity and many other organisms on Earth. Just a lack of oxygen for about 5 minutes can cause permanent brain damage that cannot be recovered. Despite this, not everyone knows when this third most abundant element in the universe originated. Let’s explore together.
Oxygen is the most crucial element for the survival of humanity.
For the first half of Earth’s history—about 2 billion years—there was no oxygen at all, but that does not mean there was no life. There is still considerable debate regarding the main biological factors in the “pre-oxygen” world, and researchers are searching for clues in the oldest sedimentary rocks on our planet.
Scientists are still uncertain about how much nitrogen was provided to our planet by the initial mineral rain. However, around 4.3 billion years ago, Earth’s hellish conditions began to cool down. The time for water accumulation was long enough to create geochemical reactions, precursors to biochemical phenomena, forming a dense atmosphere primarily composed of carbon dioxide and nitrogen.
Volcanic activity also released streams of oxygen, but it quickly transformed into other gas forms. Thus, for the first billion years, Earth had almost no oxygen until the Great Oxygenation Event (GOE) occurred. The surge in oxygen concentration was mainly due to cyanobacteria, also known as blue-green algae—photosynthetic bacteria that release oxygen. When and how this oxygen-producing bacteria emerged is still not well understood, as the GOE event coincided with global glaciation, mineral upheaval, and the flourishing of new species.
Dr. Dominic Papineau from the Carnegie Institution for Science in Washington stated: “We don’t know what the cause and consequences are. Some events happened simultaneously, so the story remains unclear.” To help address this geographical question, Papineau is studying the formation of banded iron formations, or BIFs, sedimentary rocks formed at the bottom of ancient seas. Papineau’s research, funded by NASA’s Astrobiology Program, focuses on certain minerals within BIFs that may be closely related to the life (and death) of ancient bacteria.
Image of a banded iron formation specimen at the Australian Museum of Natural History.
The iron minerals in BIFs are the largest source of iron ore in the world. However, these rocks have much more value beyond steel-making. Geologists mine them for their rich historical records spanning from 3.8 billion to 0.8 billion years ago. Nevertheless, the origin of the oldest BIFs remains a mystery. Scientists believe they required the support of organisms to form, but which organisms? Single-celled marine life leaves no bones or shells for us to study, but Papineau suggests there may still be geochemical minerals or fossils within BIFs.
He has discovered carbon materials in BIFs related to apatite, a phosphate mineral often closely associated with biology. This means that what formed BIFs is still present in their very products. To verify this, Papineau’s research team will study the carbon in BIFs and compare it with other carbon minerals of non-biological origin, including minerals found in a Martian meteorite.
Additionally, Professor Andreas Kappler from the University of Tübingen in Germany, who is also interested in this research, stated: “This research has the potential to prove that bacterial biomass was linked and deposited alongside iron minerals.” It is highly likely that the bacteria forming BIFs were cyanobacteria since the oxygen from these bacteria oxidized iron in the seas before the GOE event. But if cyanobacteria appeared long before the GOE, why did it take hundreds of millions of years for the oxygen they released to accumulate in the atmosphere?
Professor Andreas Kappler.
Papineau and his colleagues may have found part of the answer within the complex interplay between biology and geology. Oxygen from cyanobacteria may have been destroyed due to the dominance of methane. These two gases react to form carbon dioxide and water. Papineau explains: “Oxygen could not accumulate in a methane-rich environment.”
Methane is thought to originate from bacteria known as methanogens, which release methane after consuming carbon dioxide and hydrogen. In this case, methanogens and cyanobacteria shared ancient seas, but methanogens were dominant— their methane release suppressed oxygen and warmed the planet through the greenhouse effect. However, until near the time of the GOE, these organisms began to decline, and oxygen from cyanobacteria filled the atmosphere that had depleted methane.
Linking the GOE event with the decline of methanogens has been previously mentioned, but there is little evidence supporting a hypothesis that the disappearance of nickel within BIFs caused this issue. However, recently Papineau and colleagues reported in the journal Nature that nickel concentrations in BIFs significantly decreased around 2.7 billion years ago. Nickel concentrations in the seas dropped by 50% just before the GOE occurred. This is significant because methanogens depend on nickel: it is a central ingredient for metabolic enzymes involved in methane formation. When nickel concentrations dropped, methanogens were “starved,” and they gradually disappeared over time.
Image of methanogen bacteria under an electron microscope.
The nickel scarcity situation makes the pre-GOE development of cyanobacteria more plausible, but more evidence is still needed to confirm this. Kappler believes that studying the origins of the oldest BIFs could tell us when life began to develop the ability to produce oxygen and thus change the world forever.
Oxygen was discovered by Swedish pharmacist Carl Wilhelm Scheele in 1772 by heating copper oxide and a mixture of several nitrates. Scheele called oxygen “fire air” because it was the only gas known to support combustion at that time. He wrote a report on this discovery in a manuscript titled Treatise on Air and Fire, which he then sent to a publisher in 1775. This document was subsequently published in 1777. The systematic name for the element oxygen is octium.
Free oxygen hardly existed in Earth’s atmosphere before ancient archaea evolved around 3.5 billion years ago. Free oxygen first appeared in large amounts during the Paleozoic Era (between 3.0 and 2.3 billion years ago). In the first billion years, any free oxygen produced by these organisms combined with dissolved iron in the oceans to form banded iron formations. As this oxygen sank and became saturated, free oxygen began to escape as gas from the oceans around 2.7 billion years ago, reaching 10% of current levels about 1.7 billion years ago.
The presence of large amounts of dissolved and free oxygen in the oceans and atmosphere may have pushed anaerobic organisms to the brink of extinction during the Great Oxygen Catastrophe about 2.4 billion years ago. However, cellular respiration using oxygen allowed aerobic organisms to produce more energy-carrying ATP molecules than anaerobic organisms, enabling aerobic organisms to dominate Earth’s biosphere.
Since the beginning of the Cambrian period 540 million years ago, oxygen levels have fluctuated between 15% and 30% by volume. Toward the end of the Carboniferous period (300 million years ago), atmospheric oxygen levels reached their peak at 35% by volume, contributing to the large size of insects and amphibians at that time. Human activities, such as burning 7 billion tons of fossil fuels each year, have had very little impact on the free oxygen content in the atmosphere. At the current rate of photosynthesis, it may take about 2,000 years to produce all the oxygen in the current atmosphere.
Will Earth ever lose its oxygen?
As long as the sun shines, plants bloom, and photosynthesis occurs vigorously, our planet will maintain a certain level of oxygen in the atmosphere. However, this balance will never be permanent. According to scientists’ predictions, in about 1 billion years, solar radiation will be strong enough to separate carbon dioxide. If there isn’t enough gas, the process of photosynthesis will be hindered, leading to a significant decrease in oxygen levels.
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